Desorption Temperature Range Research Articles

Unveiling the dynamic thermal separation process of CO2 on the surface of calcium oxide: An ab-initio molecular dynamics study with experimental verification

Heating to release CO2 captured by Calcium oxide is one of the crucial steps in CO2 capture technology. However, the molecular mechanism underlying CO2 thermal desorption and the impact of CaO hydration on CO2 desorption remain unclear. Based on ab initio molecular dynamics (AIMD), a comprehensive analysis of the desorption and regeneration mechanism of carbonized CaO surfaces was conducted. Temperature is the primary factor responsible for CO2 thermal desorption on CaO surfaces. Simulations of CO2 thermal-dynamic desorption indicate that the desorption temperature range of CO2 from a dry CaO surface was between 400 and 500 °C. The explicit solvent model was utilised to simulate the desorption of CO2 under hydration condition. In the temperature range of 25–800 °C, the desorption behaviour of CO2 is substantially inhibited in the presence of water layers and Ca(OH)2. Consistent with the AIMD results, the thermal desorption experiment following CO2 adsorption confirmed that the desorption temperature of CO2 increases considerably when the adsorbed sample hydrates. Consequently, the desorption process of CO2 on CaO surface was comprehensively elucidated by a combination of theoretical study and experimental validation, thereby guiding the development and regeneration of CaO-based adsorbents.

Investigation of Ce/BEA as a passive NOx adsorber: 1. The occurrences of cerium and adsorption behavior

Ce/BEA has great potential as a passive NOx absorber (PNA) to reduce the NOx emissions during the cold start phase especially in diesel engine for its high resistance to CO and suitable NOx desorption temperature range. However, as a novel material, its physical and chemical properties still remain unknown. In this work, Ce/BEA was synthesized by ion-exchange method to identify the active species in NOx adsorption, compared with aggregated Ce species in Ce/SiAlOx prepared by impregnation method. X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM) and aberration-corrected-scanning transmission electron microscopy (AC-STEM) were performed to confirm the isolated single atom formation of Ce species in Ce/BEA. UV-vis diffraction reflection spectra (DRS) and X-ray photoelectron spectroscopy (XPS) were conducted to find the difference of chemical environment between the isolated Ce species and aggregated ones. PNA performance evaluation and temperature programmed reduction of hydrogen (H2-TPR) results show the high NOx storage capacity and active oxygen species quantity in Ce/BEA. It is also found that the main NOx adsorption species are Ce4+–O∗ rather than Ce3+. NOx-diffuse reflectance infrared Fourier transform spectroscopy (NOx-DRIFTS) confirms that the bidentate nitrite species are the critical NOx adsorption intermediates and the conception of NOx adsorption and desorption processes is proposed.

Catalytic-CO2-Desorption Studies of BZA-AEP Mixed Absorbent by the Lewis Acid Catalyst CeO2-γ-Al2O3.

Traditional organic amines exhibit inferior desorption performance and high regeneration energy consumption. The implementation of solid acid catalysts presents an efficacious approach to mitigate regeneration energy consumption. Thus, investigating high-performance solid acid catalysts holds paramount importance for the advancement and implementation of carbon capture technology. This study synthesized two Lewis acid catalysts via an ultrasonic-assisted precipitation method. A comparative analysis of the catalytic desorption properties was conducted, encompassing these two Lewis acid catalysts and three precursor catalysts. The results demonstrated that the CeO2-γ-Al2O3 catalyst demonstrated superior catalytic desorption performance. Within the desorption temperature range of 90 to 110 °C, the average desorption rate of BZA-AEP catalyzed by the CeO2-γ-Al2O3 catalyst was 87 to 354% greater compared to the desorption rate in the absence of the catalyst, and the desorption temperature can be reduced by approximately 10 °C. A comprehensive analysis of the catalytic desorption mechanism of the CeO2-γ-Al2O3 catalyst was conducted, and indicated that the synergistic effect of CeO2-γ-Al2O3 conferred a potent catalytic influence throughout the entire desorption process, spanning from the rich solution to the lean solution.

First-principles study on the hydrogen storage properties of MgH2(1 0 1) surface by CuNi co-doping

Exploring the hydrogen storage properties on the surface of transition metal-modified MgH2 systems is beneficial to develop new hydrogen storage regions. The first-principles approach was used to study the hydrogen storage mechanism on the CuNi co-doped MgH2(101) surface. The most stable energy adsorption site for hydrogen on the surface of CuNi co-doped MgH2(101) is above the Ni atom, and the corresponding chemisorption energy is −0.51 eV. The distribution of charge densities indicates substantial charge exchange occurs between the hydrogen molecule and Ni atom, while partial density of state analysis reveals orbital hybridization between the H-s (H2) and Ni-d orbits. Furthermore, molecular dynamics simulations indicate that the temperature range (473 to 573 K) of hydrogen desorption on the surface is similar to previous experimental results. Therefore, the (101) surface of CuNi co-doped MgH2 can be well matched with itself to obtain the additional hydrogen storage region.

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Enhancement in the hydrogen storage capability of borophene through yttrium doping: A theoretical study

In this study, we conducted first-principles density functional calculations to investigate the effect of Yttrium (Y) doping on β12-Borophene for hydrogen storage. The negative adsorption energy results proved that hydrogen molecules adsorption on Y-doped β12-Borophene (Y@Borophene) monolayer is exothermic and thermodynamically stable. The obtained adsorption energy results proved that the doped Y atoms attached strongly on β12-Borophene surface and don't tend to form a metal cluster. Moreover, results indicate that Y@Borophene can bind up to six hydrogen molecules with an average adsorption energy of −0.141 eV/H2. The adsorption energy results between Y@Borophene complex and hydrogen molecules ranged from −0.133 eV to −0.178 eV which is an acceptable range for an ideal H2 storage material. The Y@Borophene can lead the hydrogen gravimetric density to exceed the 5.5 wt% target of US Department of Energy. Moreover, the obtained electronic properties exhibit the charge transfer which occurred from the Y atom to boron atoms of borophene and from hydrogens to Y atom. The projected density of states (PDOS) analysis verifies the orbital hybridisation which primarily occurs between B-p, H-s, and Y-d orbitals, indicating the potential of hydrogen adsorption capability. Molecular dynamic simulation results confirmed that the desorption temperature range of Y@Borophene is between 186 and 334 K and had a great H2 desorption performance in the ambient temperature that is ideal for vehicle fuel cell operation. Therefore, this theoretical study presents the Y@Borophene is a prospective material for hydrogen storage system.

A standard function to evaluate optimal absorption and desorption temperature of SO2 absorbent: Taking amine alkyl organosilicon as example

A low viscous and high thermal stable dibutyl-(1,1-dimethyl-3,3,3-triphenyl-disiloxanylmethyl)-amine (DDTDA) was synthesized by two steps reaction. Its reaction enthalpy and entropy change with SO2 were found to be −85.39 kJ/mol and −244 J mol−1 K−1, whose absolute value are much higher than those of ionic liquids (ILs) and deep eutectic solvents (DESs). An objective function was proposed to balance reversible capacity and regeneration sensible heat consumption per unit absorption capacity. Based on it, the optimal absorption and desorption temperature of DDTDA were calculated and the temperature difference was found to be much lower than those of ILs and DESs, which implied its regeneration sensible heat is the lowest. According to the function, the traditional method to evaluate two absorbents by simply comparing their capacities at a certain temperature is unscientific. Different absorbents have different optimal absorption and desorption temperature range.

Improving NOx storage and CO oxidation abilities of Pd/SSZ-13 by increasing its hydrophobicity

When Pd is atomically dispersed in hydrophilic SSZ-13, it is readily hydrated to form Pd-hydrate ions. The formation of Pd-hydrate ions from dehydrated Pd ions has been reported to greatly hamper the NOx storage capacity. In this study, the concentration of dehydrated Pd ions in Pd/SSZ-13 was increased by making the sample more hydrophobic. Hydrophobic Pd/SSZ-13 was synthesized by inducing dealumination in hydrophilic Pd/SSZ-13 through the hydrothermal treatment at 750 °C, while the atomic dispersion of Pd was confirmed in both hydrophilic and hydrophobic Pd/SSZ-13 samples. Hydrophobic Pd/SSZ-13 displayed the improved NOx storage capacity in the desirable NOx desorption temperature range and the enhanced rate of NOx adsorption than hydrophilic Pd/SSZ-13. Hydrophobic Pd/SSZ-13 also displayed the better CO oxidation ability (shifting the temperature of 50 % CO conversion to the lower temperature by 71 °C) than hydrophilic Pd/SSZ-13. These improvements would have the important implications in developing Passive NOx Adsorbers.

Fast synthesis of Al fumarate metal-organic framework as a novel tetraethylenepentamine support for efficient CO2 capture

In this study, a rapid synthesis of Al fumarate metal-organic framework (AlFu) at 25 °C for 1 min has been reported. The synthesized AlFu has been impregnated by different amounts of tetraethylenepentamine (TEPA) to build novel CO2 adsorbents. AlFu before and after functionalization was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and nitrogen adsorption/desorption isotherms (BET). The results showed the introduction of TEPA into AlFu was successfully achieved by impregnation. The CO2 adsorption performances of AlFu and TEPA@AlFu were investigated by the TGA method. The effect of adsorption temperature, TEPA loading and CO2 partial pressure on the adsorption performance was studied. The results showed that the optimum adsorption temperature of TEPA@AlFu is 75 °C, and increasing the loading amount of TEPA will enhance the CO2 adsorption capacity and decrease the adsorption rate. High CO2 partial pressure is good for the adsorption process, and the highest CO2 adsorption capacity of 4.10 mmol/g was obtained at 75 °C in a pure CO2 atmosphere for the AlFu loaded with 60 wt% TEPA. The studies of adsorption kinetics show the fractional-order kinetic model fitted well with the CO2 adsorption experiment data. Moreover, the CO2 adsorption capacity of 60TEPA@AlFu sorbent declined only 2.81% after 10 adsorption-desorption cycles tested in the temperature range of CO2 adsorption (75 °C) and desorption (110 °C).

On the compatibility of porous surfaces with cryogenic vacuum in future high-energy particle accelerators

Recently, pulsed laser processing of Cu samples has been demonstrated to produce rough surfaces whose structuring at the nanoscale ensures an impressive reduction of the secondary electron yield. This feature has an undoubted appealing for applications in future high energy particle accelerators. However, the effective application of such laser treated surfaces in this context requires a rigorous evaluation of their vacuum behavior, especially when used at cryogenic temperatures. To this aim, here, we compare thermal programmed desorption between 20 and 70 K by dosing Ar multilayers of different thicknesses on a laser treated copper substrate and on its flat counterpart. Our results highlight that the spongelike structural features confer to the laser treated sample's non-negligible effects due to the gas-substrate interaction. This results in a much vaster and higher desorption temperature range with respect to what is observed from the flat substrates. This evidence could render it very difficult to find temperature intervals for which detrimental vacuum transients could be avoided in the cryogenic beam pipes. On these bases, although the electron cloud mitigation efficiency has been settled, before definitely including porous surfaces in any cryogenic machine design, all the consequences of having a rough rather than a flat wall should be carefully evaluated.

BN-analogue of [2,2]paracyclophane functionalized with Sc and Ti for hydrogen storage

Use of metal functionalized molecules for reversible hydrogen storage is well established due to their high gravimetric hydrogen storage capacity. We study BN-analogue of [2,2]paracyclophane (BNP22) containing two borazine rings and functionalized with Sc and Ti atoms to interpret its hydrogen binding capacity. First principles calculations based on density functional theory suggest that BNP22-2Sc and BNP222Ti systems can have a gravimetric density as high as 8.9 and 9.9 %, respectively. The BNP22-2Sc system can be operated under ambient thermodynamic conditions within the allowable pressure range of 3–30 atm and van ‘t Hoff desorption temperature range of 219–438 K as confirmed from molecular dynamics and occupation number studies. Both the systems establish Brønsted-Evans-Polanyi relation with BNP22-2Sc having significantly less activation energy of 0.38 eV. We discuss the energetic stability of these systems with respect to vibrational frequency, absolute hardness, and transition states. Consistent with 2020 targets set by the DOE, BNP22-2Sc proves to be budding hydrogen storage material.

Thermodynamic and cycle model for MEA-based chemical CO2 absorption

Low energy consumption is one of the most critical factors for an ideal carbon capture solvent. Numbers of studies have been carried out focusing on the development of novel chemical solvent replacing conventional monoethanolamine (MEA) solvent. However, there is no complete research framework to evaluate and explain the energy performance for different carbon capture technologies from the thermodynamic perspective. This study presents a comprehensive thermodynamic analysis on a typical MEA-based chemical absorption (CA) process. A MEA-based CA cycle is established based on the vapor-liquid equilibrium property of MEA-CO2-H2O system. Further energy efficiency analysis is conducted taking into account the heat of CO2 absorption as well as liquid heat capacity. Results show that among the three parts of energy duty of absorption heat (Qabs), sensible heat (Qabs), and water evaporation heat (Qvap), Qabs is quite stable along the researched desorption temperature range between 373 to 293K. However, the Qvap and Qsens show opposite variation trend with the increase of temperature. For an approximate idea cycle, Qsens is always the dominate factor leading to the increasing of total energy duty with the growth of temperature. However, for a real cycle, Qvap is becoming increasingly important with the increase of the partial pressure ratio for rich solvent.

The effect of active oxygen species in nano-ZnCr2O4 spinel oxides for methane catalytic combustion

The nano-ZnCr2O4 spinel oxides was synthesized by a ethylene glycol mediated solvothermal method. Catalytic combustion of methane test showed that an excellent activity over nano-ZnCr2O4 with T10% = 300 °C and T90% = 400 °C. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption measurements (BET) indicated that a uniform nano-ZnCr2O4 spinel oxides particles with the high surface area (96.2 m2 g−1) was successfully synthesized. Oxygen temperature programmed desorption (O2-TPD) profile revealed there were two obvious desorption of oxygen species from nano-ZnCr2O4 in the range of 300–400 °C and 500–700 °C. It was clear that the desorption temperature range of the first oxygen species coincided with the methane catalytic combustion temperature. X-ray photoelectron spectroscopy (XPS) analysis exhibited that Cr6+ was present in the lattice of ZnCr2O4 apart from Cr3+. High valence cations of chromium in crystal lattice probable caused the presence of interstitial oxygen species in the structure to maintain the electroneutrality. Additionally, Raman spectra proved that there is the interstitial oxygen species in the crystal lattice of ZnCr2O4. Therefore, the excellent catalytic activity for methane combustion was contributed to the flexible interstitial oxygen in the ZnCr2O4.

Effect of vanadium alloying on irradiation performance of tungsten under 60 keV helium irradiation

This work is a comparative study aiming to compare blistering and desorption behaviors of pure tungsten (W) and tungsten-vanadium alloy (W-V) after 60 keV helium (He) irradiation. Pure tungsten and tungsten-vanadium alloy, with a mass fraction of 5% V, were fabricated through powder metallurgy, then underwent irradiation of 60 keV He2+ ions at a fluence of 1.04 × 1022 m−2. X-ray diffraction and X-ray photoelectron spectroscopy were performed before irradiation to characterize the microstructures of the two specimens, while after the irradiation, scanning electron microscopy and thermal desorption spectroscopy were carried out to investigate blistering and desorption behaviors. The results indicate helium blistering of tungsten could be effectively mitigated with the addition of an appropriate proportion of vanadium. In the desorption temperature range of 300 K–1300 K, desorption of helium in the tungsten-vanadium alloy was also smaller than in pure tungsten. Alloying tungsten with 5 wt% of vanadium may have improved irradiation resistance compared with pure tungsten.

Performance evaluation of CO 2 capture with diethyl succinate

Abstract Diethyl succinate (DES) is a new and highly efficient carbon dioxide (CO 2 ) absorption solvent. Vapor-liquid equilibrium data for the CO 2 + DES system were obtained experimentally from 288.15 K to 318.15 K by the gas-phase recirculation method, and were modeled using the Kritchevsky-Kasarnovsky model and Peng-Robinson equation of state. The vapor-liquid equilibrium data of the DES system were compared with those of the diethyl carbonate (DEC) and dimethyl carbonate (DMC) systems, and Henry constant was found to follow DES 2 absorption capacity of DES is better than that of the DEC and DMC. A continuous absorption-desorption experimental setup was established for the CO 2 -DES system to determine the optimum operating conditions of a liquid-gas ratio of 1.337, an absorption temperature range from 291.15 to 293.15 K, a desorption temperature range from 433.15 to 443.15 K, and a nitrogen (N 2 ) flow of 0.5 NL/min. The DES system costs less than the DEC and DMC systems when using N 2 gas-stripping desorption. A novel desorption process with compression and condensation was used to regenerate solvent and to simplify the process. This system costs less than those for thermal desorption, and gas-stripping desorption. The results from the DES system were better than those of the DMC and DEC systems. DES shows potential as a CO 2 absorbent.

Microstructure and He desorption behaviors of He charged FeCrNi-based films fabricated by direct current magnetron sputtering

He-charged FeCrNi-based films were prepared at different temperatures in a mixed atmosphere of He and Ar by direct-current magnetron sputtering method. X-ray diffraction and energy dispersive spectrometry analysis confirmed the typical austenitic structure of the deposited FeCrNi films and the compositions were in good accordance with 304 stainless steel target. Cross-sectional scanning electron microscopy images revealed the dense columnar nanocrystalline structure of the fabricated FeCrNi films. Nanoindentation measurements showed that the film fabricated at 300°C exhibited the highest hardness value of 11.5GPa. He desorption from FeCrNi-based films was traced by thermal desorption spectroscopy; the relatively low He desorption temperature range (150°C–450°C) implied that the charged He atoms were mainly located in interstitial sites of FeCrNi-based films.

Defect production and deuterium retention in quasi-homogeneously damaged tungsten

To understand the deuterium (D) bulk retention behavior in plasma facing materials under reactor-relevant conditions, tungsten (W) foils were irradiated with 122MeV 20Ne ions and then exposed to D2 gas at 773K. A quasi-homogeneous distribution of atomic displacement damage to 0.3dpa within a depth of 50μm was produced in W using an energy degrader in the irradiation chamber. Results of positron annihilation lifetime spectroscopy showed a long positron lifetime component of ∼400ps appeared after irradiation, indicating the formation of vacancy clusters with up to 12 vacancies in W. Thermal desorption spectra showed a broad D desorption temperature range (730–1173K) with a high release peak at ∼1010K for the irradiated W specimens. The amounts of D retained in the irradiated W were significantly larger than the annealed ones, which could be attributed to the trapping effects of the vacancy clusters formed by cascade collisions and the clustering of mono-vacancies.

Investigation of hydrogen storage in MWCNT–TiO2 composite

The hydrogen storage capacity of MWCNT–TiO2 composite has been evaluated in the present work. The composite has been prepared by means of ultrasonication followed by drop casting on substrates. Morphology, structural and functional group studies of the prepared samples are carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Then, the samples are hydrogenated in the hydrogenation chamber as a function of time. Hydrogen storage capacity of the composite sample is found to be 0.9wt% at 100°C. Hydrogen uptake of the composite is accounted for the spillover mechanism in CNTs–metal oxide composite. Desorption temperature range, activation energy of desorption, binding energy of hydrogen are determined from thermogravimetric (TG) analysis.

Water Soluble Polymer-SWCNT-Based Composite for Hydrogen Storage

In this study, water soluble polymers such as poly vinyl alcohol (PVA) and poly vinyl pyrrolidone (PVP) were chosen as the base material for hydrogen storage with the aim of producing recyclable and water-soluble polymer-based hydrogen storage material. Initially, the polymers were acid treated using concentrated hydrochloric acid (conc. HCl) to incorporate Cl ions into the polymeric matrices. Furthermore, single-walled carbon nanotubes (SWCNTs) were added to those acid-treated polymers by means of ultrasonication in an aqueous medium as the composite material to increase the hydrogen adsorption. The homogenous composite solution resulted from ultrasonication was then made in the form of film by using the general spin-coating technique. Then, the composite films were hydrogenated in Seiverts' like hydrogenation setup. The preliminary results on hydrogen storage capability of the polymer-SWCNTs composite materials and desorption temperature range of hydrogen are reported. The prepared composite films exhibit good water-soluble properties and recyclability, i.e., they can be formed and dissolved in water. Hydrogen storage in these acid-treated polymer-SWCNTs composite is reported here for the first time. The presence of Cl ions and the adsorption sites offered by SWCNTs were responsible for hydrogen binding in the composite films. The nature of binding of hydrogen in the composite films was found to be weak chemisorption.

Preparation of La-Mg-Ni Hydrogen Storage Composite Alloys by Mechanical Alloying

LaNi5-xwt%Mg hydrogen storage alloys with different Mg content were made from pure La, Mg and Ni metal powder by mechanical alloying, selecting appropriate ball-milling parameters in 0.4MPa hydrogen atmosphere. The characterizations for hydrogen storage alloy show that a multi-phase alloy composed of MgH2, LaH3, Mg2NiH4 and Ni was obtained, the alloy have two hydrogen desorption temperature range, and the alloy with 25wt% Mg content can desorb hydrogen up to 4.02wt%.